As pressure-sensitive adhesives used for pressure-sensitive adhesive products each having a pressure-sensitive adhesive layer on at least a part of a surface of a base layer, such as pressure-sensitive adhesive sheets, pressure-sensitive adhesive films and pressure-sensitive adhesive tapes, solution type pressure-sensitive adhesives comprising base polymers, such as rubber-based pressure-sensitive adhesives and acrylic pressure-sensitive adhesives, have been frequently used in the past. In addition thereto, hot-melt type pressure-sensitive adhesives and aqueous emulsion type pressure-sensitive adhesives have been also used in recent years. Of these, acrylic pressure-sensitive adhesives have been widely used because they are excellent in transparency, weathering resistance and durability. As the acrylic pressure-sensitive adhesives, adhesives comprising acrylic block copolymers have been proposed from the viewpoints of coating properties and pressure-sensitive adhesion properties. For example, in a patent literature 1 and a patent literature 2, pressure-sensitive adhesives containing an acrylic block copolymer having excellent hot-melt processability and a tackifying resin have been proposed. In a patent literature 3, a pressure-sensitive adhesive using an acrylic block copolymer having a block composed of 2-ethylhexyl acrylate and having excellent holding power has been proposed. In patent literatures 4 and 5, pressure-sensitive adhesive sheets using an acrylic block copolymer as a base polymer and obtained by co-extrusion have been proposed.
The pressure-sensitive adhesives described in the patent literature 1 and the patent literature 2 had problems of insufficient cohesive force at high temperatures and insufficient durability such as insufficient holding power. The pressure-sensitive adhesive sheets of the patent literatures 3 and 4 were excellent in moldability in the co-extrusion process, but they had low adhesive force and sometimes had defects such as peeling in the durability test. In the patent literatures 1 to 4, a study of durability under the wet heat conditions was not made. The pressure-sensitive adhesive described in the patent literature 5 had excellent holding power, but there was room for improvement in adhesive force to glass.
With wide spreading of uses of the pressure-sensitive adhesives in recent years, much higher ability on the properties such as durability has been required, but satisfactory ability has not been obtained in the aforesaid pressure-sensitive adhesives containing acrylic block copolymers. With regard to pressure-sensitive adhesives satisfying also whitening resistance and low adhesion acceleration, a study has been hardly made, and it is difficult to satisfy the requirements in the prior art.